CHICAGO (AFP) - A Kentucky county clerk sought relief on Thursday from a court injunction that requires her to issue same-sex marriage certificates, insisting that it would violate her religious freedom.

A smattering of counties across the Bible Belt initially refused to provide same-sex marriage licences on religious grounds in the wake of the Supreme Court's landmark June 26 ruling which legalised gay marriage across the United States.

Most relented in a matter of days.

Rowan County Clerk Kim Davis did not.

She stopped issuing any marriage certificates at all and argued the policy could not be considered discriminatory if it applied to everyone.

A federal judge disagreed in a 28-page ruling on Wednesday in which he found the policy unconstitutionally placed an undue burden on local residents and set a bad precedent.

"Her religious convictions cannot excuse her from performing the duties that she took an oath to perform as Rowan County Clerk," Judge David Bunning wrote as he ordered Davis to issue marriage licences.

Davis disagreed in a motion seeking to block Bunning's order until her appeal is heard.

"If she is forced to authorise and approve a SSM (same-sex marriage) licence, no one and no court can unring that bell," her lawyers wrote.

"That searing act of validation would forever echo in her conscience - and, if it happened, there is no absolution or correction that any earthly court can provide to rectify it."